1. Field of the Invention
This invention relates to, and has as its principal object provision of, a novel high-yield process for the preparation of o-, m-, and p-phenylenediamine by the amination of the corresponding iodoaniline with ammonia at low to moderate temperatures in the presence of a copper catalyst. It also provides a process for the electrolytic preparation of p-iodoaniline, the key intermediate used here in the amination to prepare p-phenylenediamine, and a cyclic process combining the amination and recovery of iodine values with the electrolysis.
2. Relation to the Prior Art
Replacement of aromatic halogen atoms by amino groups is not a new reaction. p-Phenylenediamine has been prepared from p-dichlorobenzene (D. R. P. 202170 (1907)) and from p-chloroaniline (D. R. P. 204848 (1908)) by reaction with aqueous ammonia at 180.degree.-200.degree.C in the presence of a copper(II) sulfate catalyst. Cuprous iodide has also been used as a catalyst to convert p-dichlorobenzene to p-phenylenediamine (Quick, J. Am. Chem. Soc., 42, 1033 (1920)) at 200.degree.C with aqueous ammonia. The use of anhydrous ammonia in alcohol gave no product.
Chloro-, bromo- and iodobenzene are all converted essentially completely to aniline at 180.degree.-200.degree.C with aqueous ammonia and "copper sulfate or other copper salt" catalyst (Rodd, "Chemistry of Carbon Compounds", Elsevier Publishing Co., 1954, Vol. III, Part A, p. 159). Higher conversions of the activated chlorine atom in p-nitrochlorobenzene to an amino group were obtained with 60% aqueous ammonia than with anhydrous ammonia (IGF-Hoechst BIOS Final Report No. 1477, Item No. 22).
Miller, Kujawa and Campbell, J. Am. Chem. Soc. 92, 2821 (1970) describe the electrolytic iodination of aromatic hydrocarbons using iodine in acetonitrile medium. This appears to be the closest art to the electrochemical aspect of the present invention, an iodination process using iodide ion and aniline in an aqueous medium.
It has not been known heretofore to convert iodoanilines to phenylenediamines by reaction with ammonia or to electrolyze aniline to p-iodoaniline with ammonium iodide.